a) Field of the Invention
The present invention relates to a method for making marks in a transparent material, and more particularly, to a method for making marks in a transparent material using laser beam.
b) Description of the Related Arts
Method for making marks by forming indentations in the surface of an object to be marked, such as a transparent glass substrate, for example, by means of the ablation of a laser beam, are known. Using such methods, there is a risk that minute cracks may occur in the surface of the object to be marked and that fragments thereof may enter into the production line. Furthermore, when making marks by means of the ablation effect, deposits called xe2x80x9cdebrisxe2x80x9d adhere to the vicinity of the fabricated marks. The surface of the (glass) substrate must therefore be washed in order to remove the debris.
Japanese Patent JP-B Hei 7-69524 discloses a method for causing a pattern to appear inside a plastic material by focusing a laser beam on the inner portion of a transparent plastic to cause burn marks therein. This method is limited to making marks in materials in which burn marks can be made by a laser beam, such as plastics, for example.
Japanese Patent JP-A Hei 3-124486 discloses a method for making marks by focusing a laser beam on the inner portion of a glass, without harming the surface thereof. According to this method, a laser beam is directed onto the inner portion of a glass material whose inner breakdown threshold is 5-20 times the surface breakdown threshold, such that the breakdown threshold is exceeded in the inner portion of the glass without exceeding the breakdown threshold on the surface thereof. In an embodiment of this method, plastic was used as the material to be marked, and melting and degeneration, etc. were produced across a range of 20-40 xcexcm diameter and 100-250 xcexcm depth.
However, with glass material having approximately the same breakdown threshold in the inner portion and at the surface thereof, it is difficult to shine a laser beam such that the threshold value of the inner portion only is exceeded. If the threshold value at the surface is exceeded, then marking will occur on the surface.
Japanese Patent JP-A Hei 4-71792 discloses a method for making marks whereby the inner portion of a transparent material is selectively made opaque by irradiating a laser beam onto the transparent material such that it focuses on the inner portion thereof. According to this method, the transparent material is made opaque by isolated breakdown. In an embodiment of this method, the inner portion of a quartz substrate approximately 2.3 mm thick was made opaque over a range of several 100 xcexcm, this being identifiable as a white mark when viewed from the surface of the material. Since it is difficult to control the depth of focus of the laser beam accurately, this method cannot be used for making marks on thin transparent materials.
Furthermore, Japanese national publication of translated version Hei 6-500275 suggests the possibility of making three-dimensional marks on a relatively thick material.
Still, further, U.S. Pat. No. 5,206,486 discloses a method that comprises directing at a surface of a body a high energy density beam to which a material is transparent, and bringing the beam to a focus at a location spaced from the surface and within the body so as to cause localized ionization of the material.
The aforementioned methods for making marks on the inner portion of a transparent material enable marks to be made on relatively thick transparent materials, but they are not suitable for making marks on thin transparent substrates, or the like.
It is an object of the present invention to provide a method for making marks which is suitable for making marks on thin transparent substrates.
It is a further object of the present invention to provide a method for making marks which is not liable to generate particles, and the like, such that surface cleaning after marking is unnecessary.
One aspect of the present invention provides a method for making marks comprising the steps of: preparing an object to be marked; and making marks on the inner portion of the object to be marked, by focusing a laser beam of a wavelength that is transmitted by the material from which the object to be marked is formed on the inner portion of the object to be marked, using an fxcex8 lens.
Since an fxcex8 lens is used, it is possible to maintain an almost uniform depth from the surface of the object to be marked to the focal point, even when there is variation in the optical axis of the laser beam. Therefore, marks can be made in positions of almost uniform depth within a certain range of the object to be marked.
A further aspect of the present invention provides a method for making marks comprising the steps of: splitting a laser beam emitted from a laser source into a plurality of laser beams; and making marks by focusing the split plurality of laser beams onto a very small region of the inner portion of an object to be marked, thereby causing degeneration of the focal region of the object to be marked.
A further aspect of the present invention provides a method for making marks comprising the steps of: obtaining a plurality of laser beams; and making marks by irradiating a portion of the plurality of laser beams onto a plate-shaped material having a surface and a rear face, from the surface thereof, irradiating the remainder of the plurality of laser beams onto the plate-shaped material from the rear face thereof, and focusing the beams at a very small region of the inner portion of the plate-shaped material, thereby causing degeneration of the focal region of the object to be marked.
If the energy density of the laser beam in the very small region onto which a plurality of laser beams are focused exceeds a certain threshold value, then the object to be marked degenerates and a mark can be made in the very small region. The region where the threshold value is exceeded can be localized further compared to a case where a single laser beam is used.
A further aspect of the present invention provides a method for making marks, whereby a laser beam having a distribution of light intensity such that the light intensity increases with distance from the centre of the laser beam in an imaginary plane perpendicular to the optical axis thereof is focused on the inner portion of an object to be marked, thereby causing degeneration of the focal region of the object to be marked.
A further aspect of the present invention provides a method for making marks, whereby a laser beam having a circular ring-shaped cross-section perpendicular to the optical axis is focused on the inner portion of an object to be marked, thereby causing degeneration of the focal region of the object to be marked.
Usually, the energy of a convergent laser beam is higher in the central region of the laser beam, so the energy is liable to exceed the threshold value at which the object to be marked is damaged. In the laser beam used in the aforementioned marking method, the light intensity in the central region is weak or zero compared to the perimeter region thereof, and therefore the region where the threshold value is exceeded can be localized yet further in the direction of the optical axis of the laser beam.
A further aspect of the present invention provides a device for making marks comprising: a laser source; beam splitting means for splitting a laser beam emitted from the laser source into a plurality of partial beams; and a condenser optics system for focusing the plurality of partial beams split by the beam splitting means onto a very small region of the inner portion of an object to be marked.
If the energy density of the laser beam in the very small region where the plurality of laser beams are focused exceeds a certain threshold value, the object to be marked degenerates and a mark can be made in the very small region. The region in which the threshold value is exceeded can be further localized, compared to case where a single laser beam is used.
A further aspect of the present invention provides a device for making marks comprising: a laser source; beam shaping means for shaping a laser beam emitted from the laser source such that the light intensity of the beam falls with distance from the centre thereof in an imaginary plane perpendicular to the optical axis of the beam; and a condenser optics system for focusing the beam shaped by the beam shaping means onto a very small region of the inner portion of an object to be marked.
A further aspect of the present invention provides a device for making marks comprising: laser beam emitting means for emitting a laser beam in such a way that the region of light illumination on an imaginary plane perpendicular to the optical axis of the beam has a circular ring shape; and a condenser optics system for focusing a laser beam emitted from the laser beam emitting means onto a certain region of the inner portion of an object to be marked.
Usually, the energy at the central region of a convergent laser beam is liable to exceed the threshold at which the object to be marked is damaged. Here, since the light intensity in the central region is zero or weak, compared to the perimeter regions of the beam, the region where the threshold value is exceeded can be further localized in the direction of the optical axis of the laser beam.
A further aspect of the present invention provides a method for observing marks comprising the steps of: irradiating illumination light onto a transparent material bearing marks constituted by cracks formed in the inner portion thereof; and observing the light scattered by the marks at a position where illumination light transmitted through the transparent material is not incident.
A further aspect of the present invention provides a device for observing cracks comprising: illumination means for irradiating illumination light onto a transparent material; and light-receiving means located in a position where the illumination light from the illumination means is not incident, and a portion of the light scattered by cracks formed in the transparent material is incident.
Since the illumination light is not incident at the light-receiving means, marks can be observed under conditions providing a good S/N ratio.
A further aspect of the present invention provides a method for making marks comprising the steps of: preparing an object to be marked made from a glass material; and making marks by focusing a laser beam of a wavelength that is transmitted by the material from which the object to be marked is formed on the inner portion of the object to be marked, thereby causing change in the optical properties of the inner portion of the object to be marked.
By causing the optical properties to change, the corresponding region can be made visible. Since it is not necessary to produce cracks, or the like, generation of particles, etc. can be prevented.
A further aspect of the present invention provides a member comprising: a member made from a glass material; and a pattern formed by regions having different optical properties distributed in the object to be marked, wherein each of the regions having different optical properties is long and thin in shape.
The different optical properties are, for example, refractive index changes. The regions having different optical properties can be identified by observing them in their longitudinal direction.